1. Field of the Invention
The present invention relates to a toner useful, for example, for visualizing an electrostatic latent image formed on an image bearing member by a method such as electrophotography and electrostatic recording methods. In addition, the present invention also relates, without limitation, to a developer including a toner, a developing method using a toner and a method of preparing the toner.
Additional advantages and other features of the present invention will be set forth in part in the description that follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from the practice of the present invention. The advantages of the present invention may be realized and obtained as particularly pointed out in the appended claims. As will be realized, the present invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the present invention. The description is to be regarded as illustrative in nature, and not as restrictive.
2. Discussion of the Background
Electrostatic latent images and magnetic latent images, which are formed on an image bearing member of an electrophotographic image forming apparatus or electrostatic recording apparatus are developed with a toner to be visualized. For example, in electrophotography visual images are typically formed as follows:
(1) an electrostatic latent image is formed on a photoreceptor;
(2) the electrostatic latent image is developed with a developer including a toner to form a toner image on the photoreceptor;
(3) the toner image is transferred onto a receiving material such as papers; and
(4) the toner image on the receiving material is fixed upon application of heat, etc. to form a hard copy.
Recently, a need exists for an electrophotographic image forming apparatus and a developer therefor, which can produce high quality images. In order to produce high quality images, it is essential for the toner included in a developer to have a sharp particle diameter distribution because each of the toner particles can exhibit uniform performance and thereby fine dot images can be well reproduced.
The toners used for developing electrostatic latent images are colored particles typically including a binder resin, and a colorant, a charge controlling agent and additives which are dispersed in the binder resin. The methods for manufacturing the toners are broadly classified into pulverization methods and suspension polymerization methods.
Pulverization methods typically include the following processes:
(1) mixing a colorant, a charge controlling agent, an offset preventing agent and the like materials with a thermoplastic resin upon application of heat thereto to knead the toner constituents;
(2) cooling the kneaded mixture;
(3) pulverizing the kneaded mixture to form a color powder; and
(4) classifying the color powder to form a toner.
The toners prepared by pulverization methods have fair characteristics. However, the pulverization methods have a drawback in that only limited materials can be used as the toner constituents (particularly, as the binder resin). Namely, the kneaded mixture has to be easily pulverized and classified by conventional low-cost pulverizers and classifiers. From this point of view, the kneaded mixture has to be so brittle as to be pulverized. Therefore, the color powder, which is prepared by pulverizing a kneaded mixture, tends to have a broad particle diameter distribution. In order to prepare toner images having good resolution and half tone properties, the color powder has to be classified so as to have a particle diameter of from 5 to 20 μm. Therefore the toner yield is very low in the classification process.
In addition, it is impossible to uniformly disperse a colorant and a charge controlling agent in a thermoplastic resin when the pulverization methods are used. Uneven dispersion of toner constituents adversely affects the fluidity, developing properties, durability and image qualities of the resultant toner.
In attempting to solve such problems, suspension polymerization methods have been proposed and practically used now. The techniques for manufacturing a toner utilizing a polymerization method are known. However, the particles of toners prepared by suspension polymerization methods have a spherical form and therefore the toners have a drawback of having a poor cleaning property. When toner images have a low image area share (i.e., the percentage of the area of a toner image in a copy sheet is low), the amount of the toner particles remaining on a photoreceptor is small, and therefore a cleaning problem hardly occurs. However, when toner images have a high image area share (for example, copies of photograph images) are produced or when a toner image remains on a photoreceptor without being transferred to a receiving material due to paper jamming problems or the like, a large amount of the toner particles remains on the photoreceptor, resulting in occurrence of background fouling in the resultant or following images. In this case, when a contact charging roller is used, the toner particles remaining on the photoreceptor contaminate the charging roller, resulting in deterioration of the charging ability of the charging roller.
In attempting to solve such a problem, Japanese Patent No. 2,537,503 discloses a method in which resin particles prepared by an emulsion polymerization method are associated to prepare toner particles having an irregular form. However, the toner particles prepared by such an emulsion polymerization method include a large amount of a surfactant on or in the toner particles even after the toner particles are washed with water. Therefore, the resultant toner has poor charge stability when environmental conditions change and in addition the distribution of the charge quantity of the toner particles is broad, thereby causing background fouling in copy images. In addition, the remaining surfactant contaminates the photoreceptor and charging roller, developing roller and the like elements used in image forming apparatus, resulting in deterioration of the abilities of the elements.
Japanese Laid-Open Patent Publication No. 11-133665 discloses a toner including modified polyester having a Wadell practical sphericity of from 0.90 to 1.00.
Japanese Laid-Open Patent Publications Nos. 11-149180 and 2000-292981 disclose a dry toner and a method of producing the toner including a binder formed from an elongation and/or a crosslinking reaction of a prepolymer including an isocyanate group, and a colorant, wherein the dry toner is formed of particles formed from an elongation and/or a crosslinking reaction of the prepolymer (A) by amines (B) in an aqueous medium. However, the toner does not have both the transferability and cleanability.
Adding an inorganic particle such as a silica or titanium as the way of giving a charging to toner particles is known. However, these minute particles are buried inside the toner particles by being stirred in the developer for a long time, and the charging stability with the passage of time isn't assured. Making an inorganic particle fixed on the surface of the toner by mechano-chemical disposal is known, too. However, a bad influence is given to a fixation character because the surface of the toner becomes a film by the minute particle.
In addition, toners comprising a charge control agent in the toner composition are known. However, the charge control agent does not disperse in uniformly. Therefore, the electrostatic charge is unstable.
The use of fluorine in adjusting charge is known. For example, there is an approach to alter the toner surface with fluorine by adsorption or chemically or physically, for example using a fluorine-type surfactant. Such treatment can alter the electrostatic charge stability of toner particle, but the amount of carbon atom and fluorine atom as measured by XPS is important. When F/C is less than 0.01, there is little or no benefit, and 0.50 may be too high.